The field of the invention is generally that of roller chain pushers for a batch type allcase furnace, and more specifically, to an improved refractory hearth furnace floor arrangement for retaining an alloy chain and pusher assembly.
In typical batch type allcase furnaces, work pieces are placed in a stock tray, which is moved into the furnace chamber for heating and then into a vestibule or elevator for quenching. It is conventional to move stock trays on an alloy roller assembly supported by alloy plates and/or refractory. An alloy pusher assembly chain is held in a working area by alloy plates placed over the rollers of the chain. Such arrangements are conventionally referred to as roller rail hearths. Radiant tubes used to heat the furnace chamber are supported by alloy brackets bolted to the outside furnace wall.
At present, it is not uncommon for batch type allcase furnaces to reach temperatures of 2000 degrees F. When the conventional roller hearth is subjected to these temperatures the thermal stress coupled with heavy loads in excess of 1000 pounds will cause permanent distortion of roller rails and plates. Alloy parts have an expected life span of between 12 & 18 months when used on a continual basis at these high temperatures.
Refractory hearths are used in other heat treat processes, but are not designed to support stock while at the same time guide the stock tray in a straight line and provide a hold down area for the roller chain and pusher.
These hearths are generally used in conjunction with pushers that move stock in one direction. These pushers are either a solid hydraulic driven rod type pusher, or a chain pusher with no rollers. The chain laying down on its side, so that it braces itself against refractory material on both sides.
The problem has always been to design a hearth to hold down the chain that was both economical and long lasting, but was easy to replace. Most batch type furnaces operating at 1700 degree F. or higher require replacement of alloy 5 to 6 times during the expected 8 to 10 year life span of the refractory brick used to insulate the heat chamber walls.